The goal of these studies was to elucidate the participation of hormones and the second messengers cyclic 3', 5'-adenosine monophosphate (cAMP) or cyclic 3', 5' guanosine monophosphate (cGMP) in the regulation of tyrosine hydroxylase (TH) biosynthesis in tissues containing cells that synthesize catecholamines. Previous studies had shown that at least 3 types of receptors (beta-adrenergic, nicotinic and corticosterone receptors) were involved in the induction of tyrosine hydroxylase in superior cervical ganglion. In the carotid body the induction of TH can involve corticosterone, muscarinic and oxygen receptors. The participation in the induction of a Ca2 ion dependent activator protein is supported by the present experiments.